Comparison of S band diplexer design using multiplexer theory with coupling matrix synthesis

This paper presents a comparison between two techniques of S band interdigital diplexer design with i.e. with generalized multiplexer theory and coupling matrix synthesis. The design based on GMT, doubly terminated Chebyshev low pass filter response is used. The first two resonators of each channel are modified using formulas in GMT. The design is verified though MathCAD plots. In coupling matrix synthesis design, the general coupling matrix of each filter and coupling band width for two adjacent resonators are calculated. A novel technique is used for diplexer input design. The group delays are measured at the centre frequencies of channel filters. The physical diplexer design round rod type inter digital filter is selected. Both designs are simulated in HFSS with 2100 and 2250MHz with 100MHz channel band width.